You could edit the report and:
- Double-click on tblOperatingsystem in the table list on the right to add the table to your report.
- In the visual representation of the report in the upper section of the report builder, tick the Caption field in tblOperatingsystem.
- Add the following to the Critera column for the tblOperatingsystem.Caption expression, replacing "Windows 7" with the OS of your choice.
Like '%Windows 7%'